The present invention relates to an automotive steering system, and more particularly to a structure for supporting a steering column main shaft incorporated in the steering system.
Conventionally, a steering main shaft is generally housed in a tubular member called a "column tube" or "shift tube " and is journalled in bearings at both the upper and lower ends thereof in such a manner that the shaft is protected by the tubular member. In such a steering shaft supporting structure employing a column tube, even if any error or misalignment should occur in manufacture or assembly of the structure, thereby generating undesirable stresses therein, such stresses would be borne by the column tube and precluded from acting on the steering main shaft.
However, as a way to improve safety of the vehicle, it has recently been proposed to construct a steering main shaft as an impact absorbing type shaft which collapses and shortens axially when an axial force greater than a predetermined amount is applied thereto, and which therefore absorbs impact energy. This type of steering main shaft is not mounted within or protected by any column tube, as in conventional steering systems as described above, but is installed with its principal portion being unprotected or bared. Such a steering main shaft might be subjected to dangerous bending stresses due to unavoidable manufacturing error or misalignment involved in the structures which rotatably support it at both its upper and lower ends.